This invention relates to a process for preparing 1-chloro-1,1-difluoroethane and/or 1,1,1-trifluoroethane by fluorination of 1,1,1-trichloroethane with anhydrous hydrofluoric acid in the presence of antimony pentachloride.
1-Chloro-1,1-difluoroethane (hereinafter referred to simply as F-142b) is known to be important as a material for the production of vinylidene fluoride. 1,1,1-Trifluoroethane (hereinafter referred to simply as F-143a) as well as F-142b is useful as a refrigerant and a propellant in the aerosols industries.
It is well known that F-142b and F-143a are obtained by fluorination of 1,1,1-trichloroethane (generally called as methylchloroform) with the anhydrous hydrofluoric acid in the presence of antimony pentachloride. Known processes are, however, intended to prepare either F-142b or F-143a alone rather than to produce the both compounds in an arbitrary ratio. Needless to say, it has been often experienced that even if either of the compounds is intended to be produced, the formation of the other inevitably results since methylchloroform successively undergoes the following reactions: EQU CH.sub.3 .multidot.CCl.sub.3 + HF .fwdarw. CH.sub.3 .multidot.CCl.sub.2 F + HCl (1) EQU CH.sub.3 .multidot.CCl.sub.2 F + HF .fwdarw. CH.sub.3 .multidot.CClF.sub.2 + HCl (2) EQU CH.sub.3 .multidot.CClF.sub.2 + HF .fwdarw. CH.sub.3 .multidot.CF.sub.3 + HCl (3)
For example, W. B. Whalley describes, in J. Soc. Chem. Ind. Vol. 66, p. 427 (1946), the production of F-143a in which F-143a is formed by a relatively easy method, but makes no mention of the production of F-142b and F-143a in arbitrary ratios.
Japanese Patent Publication No. 3965/1974 discloses a process for producing F-142b, in which selective production of F-142b is successfully attained. But it does not comment upon the production of F-142b and F-143a in arbitrary ratios.
As previously mentioned, both F-142b and F-143a are useful compounds. Accordingly, there exists a need for an industrial process wherein F-142b and F-143a can be produced in a desired ratio according to demand.
In addition, known processes are not satisfactory for the production of F-143a alone. For example, in the process of W. B. Whalley, continuous production of F-143a is difficult. In this process, antimony pentachloride is reacted with anhydrous hydrofluoric acid to obtain a compound having an empirical formula, SbF.sub.3 Cl.sub.2 .multidot.2HF, which is subsequently reacted with methylchloroform to obtain F-143a.
Likewise, known processes are not satisfactory for the production of F-142b alone. For example, in the process as described in the Japanese Patent Publication No. 3965/1974, a reactor equipped with a condenser is used for the production of F-142b. In the reactor, methylchloroform and anhydrous hydrofluoric acid are interacted in the presence of antimony pentachloride under a reaction pressure ranging from 0 kg/cm.sup.2 G to 3.0 kg/cm.sup.2 G and at a reaction temperature ranging from the boiling point of F-142b to the boiling point of anhydrous hydrofluoric acid at the reaction pressure. In the condenser, the recovery of F-142b from the gas introduced from the reactor is effected at a condenser temperature ranging from a temperature lower by 10.degree. C than the boiling point of F-142b at the reaction pressure to the reaction temperature. However, the resulting F-142b which is taken out from the reaction system disadvantageously contains a substantial amount of anhydrous hydrofluoric acid. It is very difficult to recover the hydrofluoric acid from the product. In addition, removal of anhydrous hydrofluoric acid by passing the F-142b product obtained by the process into water or an aqueous alkaline solution results in a loss of the anhydrous hydrofluoric acid and as well as other useful materials. Moreover, the Japanese Patent Publication proposes to further react the anhydrous hydrofluoric acid-containing F-142b product with methylchloroform in the presence of antimony pentachloride in another reactor. However, this process requires an additional reactor and is thus poor in economy.